Capping of supramolecular curcubit[7]uril facilitates formation of Au nanorods during pre-reduction by curcumin

Enhanced Antibacterial Activity of Levofloxacin with Cucurbit[7]uril-Functionalized Gold Nanoparticles

Bacterial infection is one of the major concerns of the growing society, and over the years, different permutations and combinations of various drugs and adjuvants have been attempted, which led to considerable improvements in the efficacy of the antibacterial drugs. In this regard, macrocyclic receptors such as cyclodextrin, cucurbiturils, calixarene, etc., have played a major role by modulating the drug properties that supplement the antibacterial efficacy. In this study, we have developed cucurbit[7]uril (CB7)-functionalized Au nanoparticles (CB7AuNPs) to modulate the activity of an antibiotic, levofloxacin (LOFL). From the spectroscopic and thermodynamic changes in the LOFL, it has been established that two of the prototropic forms, LOFLH and LOFLH2+, form strong 1:1 host/guest complexes with CB7/CB7AuNP. Both these interactions led to significant upward shifts in the pKa values as well as photostability of LOFL, thereby enhancing the availability of the active form for the antibacterial activity, at the physiological pH. Further, the LOFL uptake has also been established on CB7AuNP, which retained the CB7-LOFL activity at very low concentration of the CB7 host, functionalized on AuNP. Detailed antibacterial studies of LOFL, both as complexed with CB7 and CB7AuNP, were carried out using four food-borne pathogens (Escherichia coli, S. Typhimurium, Bacillus cereus, and Staphylococcus aureus), which revealed a creditable enhancement in the antibacterial property, irrespective of the bacterium strain. These results are quite promising at this stage for the development of drugs customized for multidrug-resistant bacteria.

Microwave Synthesis of Au Nanoparticles in the Presence of Tetrahydrothiophenocucurbituril

The preparation of gold nanoparticles (AuNPs) from tetrachloroauric acid in the presence of tetrahydrothiophenocucurbit[n]uril (THTmQ[n]) has been effectively achieved in a microwave reactor. The reaction was performed in the presence of an excess of the tetrahydrothiopheno function in a partial reductant role, while the remainder formed AuNP-THTmQ[n] conjugates after the reduction was completed with formic acid. An affinity for the AuNPs by the THTmQ[n] was observed in the purification of the NPs via centrifugation, removal of the supernatant and resuspension of the conjugate.

Emerging sensing platforms based on Cucurbit[n]uril functionalized gold nanoparticles and electrodes

Cucurbit[n]urils (CB[n]s, n = 5-8, 10, and 14), synthetic macrocycles with unique host-guest properties, have triggered increasing research interest in recent years. Gold nanoparticles (Au NPs) and electrodes stand out as exceptional substrates for sensing due to their remarkable physicochemical characteristics. Coupling the CB[n]s with Au NPs and electrodes has enabled the development of emerging sensing platforms for various promising applications. However, monitoring the behavior of analytes at the single-molecule level is currently one of the most challenging topics in the field of CB[n]-based sensing. Constructing supramolecular junctions in a sensing platform provides an ideal structure for single-molecule analysis, which can provide insights for a fundamental understanding of supramolecular interactions and chemical reactions and guide the design of sensing applications. This feature article outlines the progress in the preparation of the CB[n] functionalized Au NPs and Au electrodes, as well as the construction and application of supramolecular junctions in sensing platforms, based on the methods of recognition tunneling (RT), surface-enhanced Raman spectroscopy (SERS), single-molecule force spectroscopy (SMFS), and electrochemical sensing (ECS). A brief perspective on the future development of and challenges in CB[n] mediated sensing platforms is also covered.

Liposome-based nanocapsules for the controlled release of dietary curcumin: PDDA and silica nanoparticle-coated DMPC liposomes enhance the fluorescence efficiency and anticancer activity of curcumin

Nanosystems with various compositions and biological properties are being extensively investigated for drug and gene delivery applications. Many nanotechnology methods use novel nanocarriers, such as liposomes, in therapeutically targeted drug delivery systems. However, liposome matrices suffer from several limitations, including drug leakage and instability. Therefore, the surface modification of liposomes by coating them or adding polymers has advanced their application in drug delivery. Hence, the prevention of drug release from the liposome bilayers was the main focus of this work. For this purpose, liposomes were synthesized according to a thin film hydration method by applying various surface modifications. Three different nanocapsules, N1, N2, and N3, were prepared using 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), poly(diallyldimethylammonium)chloride (PDAA) polymer, and silica nanoparticles. PDDA and silica nanoparticles were coated on the surface of liposomes using a layer-by-layer assembly method, completely encapsulating curcumin into the core of the liposome. Fluorescence spectroscopy, TGA, DLS, XRD, SEM, and zeta potential methods were used to characterize the prepared nanocapsules. Interestingly, the fluorescence of curcumin showed a blue shift and the fluorescence efficiency was extraordinarily enhanced ∼25-, ∼54-, and ∼62-fold in the N1, N2, and N3 nanocapsules, respectively. Similarly, encapsulation efficiency, drug loading, and the anticancer activity of dietary curcumin were investigated for the different types of DMPC nanocapsules. The drug efficiencies of the liposomes were established according to the release of curcumin from the liposomes. The results showed that the release of curcumin from the nanocapsules decreased as the number of layers at the surface of the liposomes increased. The release of curcumin follows the Higuchi model; thus, a slow rate of diffusion is observed when a number of layers is added. The better encapsulation and higher anti-cancer activity of curcumin were also observed when more layers were added, which is due to electrostatic interactions inhibiting curcumin from being released.

Anisotropic Gold Nanoparticles in Biomedical Applications

Gold nanoparticles (AuNPs) play a crucial role in the development of nanomedicine, principally due to their unique photophysical properties and high biocompatibility. The possibility to tune and customize the localized surface plasmon resonance (LSPR) toward near-infrared region by modulating the AuNP shape is one of the reasons for the huge widespread use of AuNPs. The controlled synthesis of no-symmetrical nanoparticles, named anisotropic, is an exciting goal achieved by the scientific community which explains the exponential increase of the number of publications related to the synthesis and use of such type of AuNPs. Even with such steps forward and the AuNP translation in clinic being done, some key issues are still remain and they are related to a reliable and scalable production, a full characterization, and to the development of nanotoxicology studies on the long run. In this review we highlight the very recent advances on the synthesis of the main classes of anisotropic AuNPs (nanorods, nanourchins and nanocages) and their use in the biomedical fields, in terms of diagnosis and therapeutics.